1. Field of the Invention
The present invention relates to a macro lens system with a long focal length, which enables photographing from infinity to life-size.
2. Description of the Related Art
In a macro lens system, the traveling distance of the focusing lens group is generally long. Moreover, if an attempt is made to provide a longer focal length in a macro lens system, the traveling distance of the focusing lens group tends inevitably to be even longer, and the weight thereof tends inevitably to become heavier. On the other hand, most of the lens systems, not limited to a macro lens system, which are to be used with automatic-focusing equipment, are required to materialize a quick movement of the focusing lens group and an weight-reduction thereof to decrease a load imposed on a power source. However, in the macro lens system disclosed in U.S. Pat. No. 5,402,268, the most object-side lens group is made moveable, and the overall length of the lens system varies accordingly; however, this arrangement is not suitable for an automatic focusing operation, and the optical performance the lens system at an intermediate magnification is not satisfactory.
In addition to the above, the macro lens system disclosed in Japanese Unexamined Patent Publication No. Hei-9-211319 has relatively preferable optical performance; however, the lens system is not suitable for an automatic focusing operation, since the lens diameter is large, the number of lens elements is large, i.e., 14 to 15 lens elements, and the weight thereof is heavier.
It is an object of the present invention to provide a small-sized and light-weight macro lens system with a long focal length, which enables photographing from infinity (an infinite photographing distance) to life-size (the closest photographing distance), and which is suitable for an automatic-focusing camera and has a high optical performance.
In order to achieve the above objects, there is provided a macro lens system with a long focal length, which includes a positive first lens group, a negative second lens group, a positive third lens group, and a negative fourth lens group, in this order from the object. Upon focusing from an infinite photographing distance to the closest photographing distance, the second lens group moves towards the image, and the third lens group moves toward the object. The macro lens system satisfies the following condition:
3.7 less than |fxc3x97m/xcex94X3| less than 9.9xe2x80x83xe2x80x83(1)
wherein
f designates the focal length of the entire lens system at an infinite photographing distance;
m designates the transverse magnification at the closest photographing distance; and
xcex94X3 designates the traveling distance of the third lens group from the infinite photographing distance to the closest photographing distance.
The macro lens system preferably satisfies the following condition:
0.85 less than |xcex94X3/xcex94X2| less than 1.5xe2x80x83xe2x80x83(2)
wherein
xcex94X2 designates the traveling distance of the second lens group from the infinite photographing distance to the closest photographing distance.
The macro lens system can be arranged to satisfy the following conditions:
0.1 less than |xcex23Exe2x88x92xcex23S| less than 0.34xe2x80x83xe2x80x83(3)
xcex23E/xcex23S less than 0xe2x80x83xe2x80x83(4)
wherein
xcex23E designates the transverse magnification of the third lens group at the infinite photographing distance; and
xcex23S designates the transverse magnification of the third lens group at the closest photographing distance.
The macro lens system preferably satisfies the following condition:
1.3 less than |xcex24| less than 1.8xe2x80x83xe2x80x83(5)
wherein
xcex24 designates the transverse magnification of the fourth lens group.
The present disclosure relates to subject matter contained in Japanese Patent Application No.Hei-11-189213 (filed on Jul. 2, 1999) which is expressly incorporated herein by reference in its entirety.